Cost-Saving Developments in Security Lighting

The new solid-state lighting technology provides added benefits to the security industry by allowing surveillance lighting to be combined with general safety lighting, dramatically cutting installation, maintenance and operational costs.

The lighting industry is not alone in benefiting from the development of high-power LEDs. Stimulated by the pioneering work of companies, the security market has fast come to recognize the benefits of LED-based illumination.

Bosch Security Systems' recent acquisition of Derwent Systems, a company that has more than 20 years of experience in developing security lighting for surveillance applications, is one example.

LED platforms have operational lifetimes up to 50,000 hours (50 times that of traditional lamps) and less than 20 percent of the power consumption for the same illumination levels. Running costs and carbon dioxide emissions can be dramatically reduced, making the solution more cost-effective and eco-friendly.

Technology EvolutionThe development of white LEDs was the big driver for the change.

Before the development of blue LEDs in the mid 1990s that made the generation of white light possible, the only LEDs available were IR and through red to green. White light was impossible to be generated at that time.

Even so, the use of LED illuminators in security started early. Before this major breakthrough in white-LED technology, security system manufacturers already made use of high-power IR LED illuminators for covert surveillance.

IR, which is invisible to the human eye, can enable true 24/7, day and night surveillance when used with a low-light camera. This security lighting was specifically designed. It initially used tungsten halogen-based illuminators and later illuminators based on IR LEDs.

Following the development of the white LED is the night-time color imaging. This became possible because the spectral output of white LEDs follows the photopic curve that describes the color response of a human eye and of a color camera more closely than incandescent light sources. Therefore, it can better produce accurate renditions of the colors in a scene.

In contrast, the spectrum of high-power sodium lamps peaks in the yellow, and metal halide lamps peak in the blue. Both are not beneficial to color pictures since they cause major shifting of the colors within the scene.

To put the potential savings provided by white LED-based systems in perspective, consider a perimeter fence of typically 50 kilometers illuminated along its length by 1 kW metal-halide safety lights every 40 meters.

This makes a total of 1250 lamps and a total power consumption of 1.25 MW. Replacing these metal-halide lamps with white LED illuminators will produce the same illumination level with only 35 W of power consumption, saving nearly 97-percent running cost in electricity.

Maintenance costs can also be reduced. Metal-halide lamps that burn for 12 hours a day will need replacements every six months, but white LED illuminators last a minimum of five years without degradation.

Moreover, the light distribution of a LED-based illuminator can be more precisely controlled than with traditional light sources, which helps eliminate light pollution and save at least 30 percent of the energy.

The safety of an area is, therefore, enhanced when this form of directional light is used, as areas are more evenly illuminated with fewer shadows.

Value-added FeaturesIn the past, separate installations were needed for security lighting and safety lighting. This is because the spectral output of high-power sodium and metal-halide lamps traditionally used for safety lighting are not suitable for color video.

However, with white LED illuminators, combining security and safety lighting in a single installation becomes possible.

An intrusion detection system developed by Tew Plus (a U.K.-based system integrator) using Bosch's systems is one example. Based on a PIR detector that activates a white-light LED illuminator, the system enables color images to be taken of an intruder and transmitted back to a central control room. The white light that floods in the area also effectively deters any potential criminal activity.

"Use of white-light LEDs enhanced our product specification immensely. Due to the low voltage and instant light, we can now provide instant video images 24 hours a day with full color," said David Farman from Tew Plus. "It also enhances the overt aspect of our product by lighting up a large area in front of the camera when an intruder is detected."

These lights can also be used as stand-alone security and safety lighting. "The distance covered and the LUX level produced are quite amazing, considering their low-voltage requirements. The system is maintenance- free, which provides us with a highly cost-effective lighting solution for our customers," said Farman.

The system has already undergone an eight-week trial with Network Rail, United Kingdom, where no repeats of incidents of vandalism or cable theft were seen.

The products are also intrinsically more robust with better shock resistance. Therefore, they are better suited for use in areas prone to vibration, such as roads, bridges, poles, pylons, wind turbines, ships and rail networks.

However, there is a common disadvantage.

The performance for almost all semiconductor devices is temperature-sensitive, and its output will degrade over time. The ageing affect is rather dramatic as LEDs degrade by around 10 percent in the first six months of operation and continue to degrade over the remainder of their lifetime.

Luckily, some illuminators can overcome this disadvantage. Camera systems can be specifically designed to combat LED degradation and temperature fluctuation.

For example, a feedback circuit can compensate for any degradation in light output caused by increasing temperatures and ageing.

This patent-pending technology is referred to as "Constant Light." The system continuously measures the light output from the LEDs and automatically adjusts the drive current to maintain light output at a constant level.

With this technology, the light output of the illuminator is guaranteed to remain constant over a temperature range of 50 degrees Celsius below and above zero.

It can cover geographical locations from Alaska to the Middle East for a period in excess of five years.

Also, the Black Diamond microrefractive lens technology delivers uniform illumination to a scene. Black Diamond ensures that all radiant energy emitted by the LEDs is directed at the scene with no upward leakage that might happen with other circular-emitting illuminators.

The illumination is also evenly distributed between the foreground and background, eliminating foreground overexposure and allowing the camera to operate correctly within its dynamic range.

The net effect of this technology is an increased dynamic range and better imaging from the surveillance system, even under extreme conditions.